1. Field of the Invention
The present invention relates to an optical device having a lens unit movable between a shooting position and a retracted position, a control method therefor, and a program for implementing the method, and more particularly to a technique for controlling extension of the lens unit.
2. Description of the Related Art
Conventionally, an optical apparatus, such as a camera, generally performs a zooming operation and a focus adjusting operation by moving a plurality of lens groups held in respective barrels, i.e. the barrels in an optical axis direction. Further, a camera is known which holds a lens barrel in its retracted state when not shooting by receiving the same in its camera body, and extends the lens barrel to a shooting position when shooting.
In a camera of this type, a variable power lens group is driven e.g. by a DC motor. Torque of the DC motor is transmitted to a drive ring having an inner periphery thereof formed with a cam groove, and the variable power lens group is extended along the cam groove in an optical axis direction.
On the other hand, the focus adjusting operation is performed using e.g. a stepping motor or the like separately provided from the drive motor for the variable power lens group. A camera has also been realized which uses a rear focus lens system disposed rearward of the variable power lens group on the optical axis as a focus adjusting lens. The term ‘rearward on the optical axis’ is intended to mean a direction opposite to a direction toward an object in front of the cameras i.e. a direction toward the inside of the camera.
Further, a technique has been proposed in which a variable power lens group disposed forward of a focus adjusting lens is retracted into a moving area of the focus adjusting lens (see Japanese Laid-Open Patent Publication (Kokai) No. 2000-194046). This technique is used to reducing distances between lens groups in the retracted state to thereby reduce the size of a camera body.
Next, a conventional operation for extending a barrel from its retracted position will be described with reference to a flowchart in FIG. 19.
When a shooting mode is selected by the user (S01), a control unit (not shown) determines, based on an output from a linear sensor or the like, whether the zoom position of the barrel is in the retracted position or in a shooting-permitting position between a WIDE position to a TELE position (S02). If the zoom position of the barrel is in the shooting-permitting position, the control unit proceeds to a step S07, described hereinafter. On the other hand, if the zoom position of the barrel is in the retracted position, the control unit causes the DC motor to rotate by a predetermined amount in a predetermined direction to thereby perform extension of the barrel holding a variable power lens, i.e. zoom driving operation (S03).
Next, the control unit temporarily stops driving the DC motor for zooming and determines whether or not a leaf switch is in “ON” state (S04). If the leaf switch is in “OFF” state, the control unit judges that an error has occurred, to stop driving of the DC motor for zooming, and executes error handling, such as warning display (S05). If the leaf switch is in “ON” state, the control unit continues the driving of the DC motor for zooming to extend the barrel to the WIDE end (S06).
When extension of the barrel to the WIDE end is completed, the control unit drives the stepping motor to thereby move the focus adjusting lens toward a photointerrupter (S07). Then, the control unit determines whether or not the focus adjusting lens has been detected by the photointerrupter (S08).
If it is determined that the focus adjusting lens has not been detected by the photointerrupter, the control unit judges that an error has occurred, to stop the DC motor and the stepping motor, and executes error handling, such as warning display (S09).
If the focus adjusting lens has been detected by the photointerrupter, the control unit acquires a count-up value of a counter for counting the drive amount of the focus adjusting lens (S10). Then, the control unit drives the stepping motor based on the acquired count-up value of the counter so as to move the focus adjusting lens to a standby position for starting an AF operation (S10). Thereafter, the control unit resets the counter.
As described above, at the start of shooting, extension of the variable power lens group is started prior to extension of the focus adjusting lens. Then, after extension of the variable power lens group to its shooting position is completed, the focus adjusting lens is extended into a space which has become empty by extension of the variable power lens group. Therefore, even when spaces between the lens groups in the retracted position are reduced as mentioned above, it is possible to avoid collision between the variable power lens group and the focus adjusting lens during extension of the lenses.
However, in the prior art described above, since the focus adjusting lens located rearward of the variable power lens group on the optical axis is extended after completion of extension of the variable power lens group, it take longer time to extend the lens barrel before it is in a shooting-permitting position.
To solve this problem, there has been proposed a technique in which extension of the focus adjusting lens is started after the start of extension of the variable power lens group and before the end of the operation (see Japanese Patent No. 2601425).
However, in the technique disclosed in Japanese Patent No. 2601425, when an external force is applied to a camera during extension of the variable power lens group and the extending operation is stopped by the external force, for example, the focus adjusting lens extended from a position rearward of the variable power lens group on the optical axis collides with the variable power lens group.